Yes, it will most likely fit your cup, see my pics.Yes it will keep your drink warm for as long as it's onIt does keep them hot hot a bit longer.But no it doesn't keep them hot hot forever BUT I'd imagen none of them do as the item itself does put out plenty of heat, it's more that cups are not really meant to transfer heat, they are supposed to do the opposite.I put cold water on and left it on, managed to warm it up to just above Luke-warm so that's what you'll get if you leave your drink for an hour, better than cold but again, not hot hot.Pretty good, worked a treat for me being slow and lazy in the morning or playing computer games and sipping every 5 mins.Does keep a tin mug slightly hotter for a bit but not a massive difference.Yeah.. for the price no buyers remorse from me.